An ion mobility spectrometer resolves ions according to different drift velocities of different ions under a uniform weak electric field. It has the advantages of high resolution speed, high sensitivity, free of a vacuum environment and convenience for miniaturization, thus being widely applied to the detection field of narcotics and explosives. A typical ion mobility spectrometer is generally composed of a sample introduction part, an ionization part, an ion gate, a migration area, a collection area, a readout circuit, a data collecting and processing part, a control part and the like, wherein the main function of the ionization part is to transform sample molecules into ions for migration and separation, thus the ionization effect has very direct influence on the performance of the spectrometer. In the prior art, the most common and most widely used ionization assembly is a 63Ni radioactive source, which has the advantages of small volume, high stability and no additional circuit, but also has the problems of narrow linear range, low ion transformation concentration and radiation pollution. Especially, the radiation pollution problem brings a lot of inconvenience to operation, transportation and management of equipment. In order to overcome the above-mentioned problems, corona discharge technology is adopted to replace radioactive source technology. Corona discharge refers to a phenomenon of gas molecule separation induced by a local strong electric field in a non-uniform electric field in the space. Ions directly generated by corona discharge are generally called reactant ions, when sample molecules with higher protons or electron affinity pass by the ionization area, the sample molecules capture the charges of the reactant ions to be ionized. In general, a corona discharge structure is relatively simple, so the cost is low; meanwhile, the concentration of charges generated by corona discharge is much higher than that of the radioactive source, thereby being beneficial to improving the sensitivity of the ion mobility spectrometer and obtaining a larger dynamic range. Application examples of corona discharge serving as the ionization source of the ion mobility spectrometer are reported in U.S. Pat. No. 5,485,016 and CA2124344 and Chinese patents CN1950698A and CN103137417A. A common corona discharge structure 100 has a discharge form of pinpoint-flat plate or pinpoint-cylinder, as shown in FIGS. 1A and 1B. The fixed tail end of a corona pin realizing discharge is usually installed on a supporting matrix, and the tail end is connected to a high voltage power supply; the other end of the corona pin is a free end (i.e., a pinpoint) and is generally a tip 102 with a very small radius of curvature (smaller than 0.1 mm). A non-uniform electrostatic field is formed in the space between a flat or cylindrical electrode and the pinpoint, such that the electric field intensity near the pinpoint is very high, and the electric field intensity of the space away from the pinpoint progressively decreases. Gas ionization only occurs in the space close to the surface of the free tip of the electrode, the ionization area is very small, thus the generated ion concentration is quite small as well; if the ionization area is increased, a higher voltage is needed, and the requirement on the high voltage power supply is very high. In addition, under the condition that only one tip discharges, the corona discharge will generate oxidation on a corona electrode, after long term operation, chemical reactions resulting from water vapor or the like in the gas will severely corrode the tip to increase the radius of curvature thereof, thus increasing the voltage threshold of the corona discharge, reducing the corona discharge stability and leading to the end of service life; furthermore, in order to achieve a smaller radius of curvature, the diameter of the pin is very small in general, the strength is quite low, thus it is very difficult to keep a higher position precision during manufacture and assembly of a product. In order to improve this situation, a multi-pin corona discharge structure is developed.
U.S. Pat. No. 7,326,926B2 describes a typical multi-pin cluster corona discharge ion source, as shown in FIG. 1C. A cluster 106 of parallel corona pins is adopted to replace a single corona pin of the typical corona discharge ion source 104; due to the design of simultaneously loading a high voltage on multiple tips of the multi-pin cluster to discharge, the problem of reduced service life of the ionization source caused by discharge failure of the single corona pin is eased to a certain degree. However, the design of simultaneously loading the high voltage on the multiple tips to discharge also has obvious disadvantages. Firstly, the high voltage is simultaneously loaded on multiple pins, electric fields formed by the pins will influence each other to reduce the electric field intensity at the pinpoints, thus a corona voltage needs to be improved, as a result, a higher requirement is proposed on the high voltage power supply; in addition, due to the processing inconsistency, the shapes and surface conditions of the tips are different, all tips cannot be guaranteed to meet a corona discharge condition, the pin with a relatively small radius of curvature firstly discharges and is gradually corroded to result in gradual increasing the radius of curvature thereof to fail to meet the corona discharge condition, and the rest pins meeting the condition begin to discharge, in this case, how many pins generate corona discharge at a moment cannot be guaranteed, with high stochastic property, so that the change of the number of ions generated by ionization is very large, resulting in unstable corona discharge, which is not conducive to the stable work of the ion mobility spectrometer.